In response to certain wavelengths of electromagnetic radiation (or “actinic radiation”), photochromic materials, such as indeno-fused naphthopyrans, typically undergo a transformation from one form or state to another form, with each form having a characteristic or distinguishable absorption spectrum associated therewith. Typically, upon exposure to actinic radiation, many photochromic materials are transformed from a closed-form, which corresponds to an unactivated (or bleached, e.g., substantially colorless) state of the photochromic material, to an open-form, which corresponds to an activated (or colored) state of the photochromic material. In the absence of exposure to actinic radiation, such photochromic materials are reversibly transformed from the activated (or colored) state, back to the unactivated (or bleached) state. Compositions and articles, such as eyewear lenses, that contain photochromic materials typically display colorless (e.g., clear) and colored states that correspond to the colorless and colored states of the photochromic materials contained therein.
The amount of a photochromic material required to achieve a desired optical effect when incorporated into a composition or article typically depends, at least in part, on the amount of actinic radiation that the photochromic material is capable of absorbing on a per molecule basis. The amount of actinic radiation that a particular photochromic material absorbs on a per molecule basis is quantitatively referred with regard to the molar absorption coefficient (or “extinction coefficient”) of the photochromic material. Photochromic materials having a relatively high molar absorption coefficient are more likely to transform from a closed-form to an open-form upon exposure to actinic radiation, than photochromic materials having a relatively lower molar absorption coefficient. Correspondingly, photochromic materials having a higher molar absorption coefficient may be used in lower concentrations in photochromic compositions and articles, than photochromic materials having a lower molar absorption coefficient, without compromising the desired optical effect.
In some applications, the amount of photochromic material that may be used or incorporated into an article may be limited for reasons including, for example, physical dimensions, solubility and/or economics. Articles having limited physical dimensions (e.g., very thin articles) may be capable of having incorporated therein only a limited and relatively low amount of photochromic material. Articles fabricated from materials in which the photochromic material has low solubility, may be capable of having incorporated therein only a limited and relatively low amount of photochromic material. Some photochromic materials are expensive, and in light of economic considerations relating to cost minimization, it may be desirable to incorporate lower amounts of photochromic material into the article. As such, photochromic materials having higher molar absorption coefficients may be desirable in applications requiring lower or minimum levels of photochromic material incorporation.
Photochromic materials, as discussed previously, are typically transformed from a closed-form (e.g., a bleached form) to an open form (e.g., a colored form) when exposed to certain wavelengths of electromagnetic radiation. In particular, many conventional photochromic materials typically undergo the closed-form to open-form transformation when exposed to electromagnetic radiation having wavelengths ranging from about 320 nanometers (nm) to about 390 nm. Such conventional photochromic materials may not be adequate for use in environments that are substantially shielded from electromagnetic radiation having wavelengths ranging from about 320 nm to about 390 nm. Certain transparencies, such as automotive windshields absorb (or act as a shield relative to) electromagnetic wavelengths in the range of 320 nm to 390 nm. As such, photochromic articles, such as photochromic eyewear, that include conventional photochromic materials, typically do not adequately undergo the closed-form (clear) to open-form (colored) transformation within the passenger compartment of an automobile (i.e., behind the windshield), because the windshield substantially absorbs electromagnetic radiation in the 320 to 390 nm wavelength range.
It may be desirable to develop photochromic materials having a closed-form absorption spectrum for electromagnetic radiation that is shifted to longer wavelengths (i.e., “bathochromically shifted”). A photochromic material having a bathochromically shifted closed-form absorption spectrum, will typically undergo the desired closed-form to open-form transformation at longer wavelengths than a conventional photochromic material. As such, in environments that are substantially shielded from electromagnetic radiation having wavelengths ranging from about 320 nm to about 390 nm (e.g., behind an automotive windshield), it may be desirable to employ photochromic materials having a closed-form absorption spectrum that is bathochromically shifted to wavelengths greater than 390 nm, which would then be capable of undergoing the desired closed-form to open-form transformation (at wavelengths greater than 390 nm).
United States Patent Application Publication No. US 2008/0103301 A1 discloses indeno-fused naphthopyrans having an electron-withdrawing, non-conjugated group bonded to the 11-position thereof.
United States Patent Application Publication No. 2007/0278461 A1 discloses indeno-fused naphthopyrans having a haloalkyl group bonded to the 13-position thereof.